It is well known that an electroconductive filler is kneaded and dispersed into an electrically insulative resin, which turns into an electroconductive resin in order to impart electroconductivity for antistatic and other purposes. As an electroconductive filler to be kneaded into a resin, an ionic electroconductive organic surfactant, a metal fiber and powder, an electroconductive metal oxide powder, a carbon black, a carbon fiber, a graphite powder and the like are generally utilized. By molding and processing an electroconductive resin composition wherein this filler has been molten, kneaded and dispersed into a resin, a molded article having a volume resistance value of 10−1 to 1012 Ω·cm can be obtained.
However, a metallic filler has the problem of a poor corrosion resistance and chemical resistance. An inorganic electroconductive filler requires a large amount of blending more than 50% by mass relative to the total mass of a composition because it is generally granular. Thus, its resin properties degrade and molding becomes difficult. Blending with a carbon black in 15% by mass or less allows for a high electroconductivity because the Ketjen Black (the registered trademark by the Ketjen Black International Co.) and an acetylene black are available, which form an electroconductive circuit with a chain-like structure. However, these are difficult to the control of dispersion into a resin and a distinct formulation and mixing technologies are required to obtain a stable electroconductivity. Even if a sufficient electroconductivity is obtained, not only a processability extremely degrades but also the physical properties of an electroconductive resin composition such as a tensile strength, a flexural strength and an impact resistance strength extremely degrade in comparison with the original physical properties of a resin free from an electroconductive filler.
In terms of an electroconductive filler, a relatively small amount of blending can also impart an electroconductivity to a resin by using a material with a high aspect ratio (length/outside diameter) in a flake form, a whisker form or a fibrous form. This is because an electroconductive filler with the higher aspect ratio forms the more effective linkage between fillers in the same amount of blending, which allows for obtaining an electroconductivity in the smaller amount.
However, even the electroconductive filler with a high aspect ratio described above such as a graphite powder in a flake form and a carbon fiber in a whisker form requires a mount more than 15% by mass to exhibit an electroconductivity, which degrades the original properties of a resin. Upon obtaining a molded article with a complex shape, a moldability and electroconductivity is inhibited with the emergence of deviation and orientation of fibers. There is also the problem such as an environmental pollution and damages on a device during the process of a semiconductor device because the carbon particles and carbon fibers readily slough away from the surface of a molded article (sloughy).
When the carbon fibers with different fiber diameters are also blended in the same amount of mass, the fiber with the smaller fiber diameter is more excellent in imparting an electroconductivity due to the more facile formation of an electroconductive circuit network among fibers. A hollow extra-fine carbon fiber, the so-called carbon nanotube has been recently disclosed, which has a fiber diameter smaller in two to three digits than that of conventional carbon fibers, and its blending into various resins, rubbers and the like has been also proposed as an electroconductive filler (Patent document 1: JP-A-H01-131251, Patent document 2: JP-A-H03-74465, Patent document 3: JP-A-H02-235945), which is regarded as an effective electroconductive filler solving the defects of the conventional electroconductive fillers.
So-called ultrafine carbon fibers collectively called as carbon nanofiber or carbon nanotube can be generally categorized into the following three nanostructured carbon materials based on their shapes, configurations and structures:
(1) Multilayer carbon nanotube (multilayer concentric cylindrical graphite layer)(non-fishbone type);
    Japanese publication of examined application Nos. H03-64606 and H03-77288    Japanese Laid-Open publication No. 2004-299986(2) Cup stack type carbon nanotube (fishbone type);    U.S. Pat. No. 4,855,091    M. Endo, Y. A. Kim etc.: Appl. Phys. Lett., vol 80 (2002) 1267 et seq.    Japanese Laid-Open publication No. 2003-073928    Japanese Laid-Open publication No. 2004-360099(3) Platelet type carbon nanofiber (card type)    H. Murayama, T. maeda: Nature, vol 345 [No. 28] (1990) 791 to 793    Japanese Laid-Open publication No. 2004-300631.
In a (1) multilayer carbon nanotube, conductivity in a longitudinal direction of the carbon nanotube is high because electron flow in a graphite network plane (C-axis) direction contributes to conductivity in a longitudinal direction. On the other hand, for inter-carbon-nanotube conductivity, electron flow is perpendicular to a graphite network plane (C-axis) direction and is generated by direct contact between fibers, but it is believed that within a resin, since inter-fiber contact is not so contributive, electron flow by electrons emitted from the surface layer of a conductive filler plays more important role than electron flow in fibers. Ease of electron emission involves conductivity performance of a filler. It is supposed that in a carbon nanotube, a graphite network plane is cylindrically closed and jumping effect (tunnel effect hypothesis) by π-electron emission little occurs.
In an ultrafine carbon fiber having a (2) fishbone or (3) card type structure, an open end of a graphite network plane is exposed in a side peripheral surface, so that conductivity between adjacent fibers is improved in comparison with a carbon nanotube. However, since the fiber has a piling structure in which C-axis of a graphite network plane is inclined or orthogonal to a fiber axis, conductivity in a longitudinal fiber-axis direction in a single fiber is reduced, resulting in reduced conductivity as the whole composition.
The so-called carbon nanotubes described above have also difficulty in uniform dispersion into a resin, and they are far from satisfactory because there are problems such as unspinnability (broken thread), filter occlusion at the discharge part of a molding machine, deterioration in the mechanical strengths such as the impact resistance of a molded article and its surface appearance due to the residue of the undispersed portion of carbon nanotubes as an aggregate in a resin. For this reason, blending and mixing the especial compositions and the particular surface modification treatments are needed, for example, optimization of resin molecular weight (Patent document 4: JP-A-2001-310994), blending with modified resin, elastomer and compatibilizing agent (Patent document 5: JP-A-2007-231219, Patent document 6: JP-A-2004-230926, Patent document 7: JP-A-2007-169561, Patent document 8: JP-A-2004-231745) and surface modification treatment of carbon nanotube (Patent document 9: JP-A-2004-323738), and the kind, composition and the like of resins are restricted, thus, further improvements are demanded.
On the other hand in terms of a resin, crystalline polyamides as typified by nylon 6 and nylon 66 are widely employed as a textile for clothing and for industrial materials or a versatile engineering plastic due to their excellent properties and easiness of melt molding; however, problems are clarified such as a property deviation by absorbing water and a degradation in acids, alcohols at an elevated temperature and hot water.
Although there is also a demand for an electroconductivity in an application employing a polyamide resin for purpose such as antistatic and electromagnetic shielding (for example, Patent document 11: JP-A-H07-207154), a problem is pointed out in decrease in an electroconductivity owing to swelling upon absorbing moisture, a hydrocarbon fuel and an alcohol in case of the conventional aliphatic polyamide resins.
However, it is known that a polyamide resin produced by employing oxalic acid as a dicarboxylic acid component, referred to as a polyoxamide resin, has a higher melting point and a lower percentage of water absorption in comparison with other polyamide resins with the same concentration of a amino group (Patent document 10: JP-A-2006-57033), which is expected to be utilized in the field where it is difficult to use the conventional polyamides due to the problem of a property deviation by absorbing water.